The invention relates to optical connectors for coupling optical fibers to opto-electronic devices, and more particularly to injection molded connectors.
Data transmission over optical fibers offers many significant advantages over metallic conductors including: long distance transmission without the need for repeaters, immunity from external electromagnetic interference, cross-talk and ground loop, high bandwidth capabilities, small size and weight, high degree of intercept security and dielectric isolation, and long term cost reduction. These desirable features of optical fiber technology have strongly stimulated efforts both in fiber optics and in supporting technologies such as optical fiber to optical device connectors.
Optical fiber connections to opto-electronic devices have often employed adhesive means such as epoxy to secure a fiber end directly to an optoelectronic device. Illustrative devices include an optical source and/or an optical detector. The connectors typically include a ferrule or the like adapted for fiber insertion therein. Another fiber to device connection comprises an optical lens such as a spherical lens or a graded refractive index (GRIN) lens positioned between the device and the end of the fiber to improve the coupling efficiency. The fiber end is typically secured in the ferrule to aid in its positioning. Some devices include the lens within the device housing and therefore do not need additional optical equipment between the fiber and device.
The above-described means for connecting an optical fiber to an opto-electronic device require active alignment of the fiber to the device to ensure proper light transmission and minimal loss due to the coupling. Active alignment may include the steps of: performing a preliminary alignment of the fiber and the device in both the axial and radial directions, performing transmission tests between the fiber and device to determine power transmission characteristics and coupling efficiency, and varying the relative orientation between fiber and device in both the axial and radial directions to maximize power transmission and coupling efficiency. After alignment, the fiber is first secured by an adhesive means such as epoxy or optical glue, followed by a curing step to set the epoxy, and then followed by a burn-in process to identify substandard connections. This procedure is time-consuming as well as inaccurate, and requires a second alignment test to ensure proper alignment in the event that small disturbances adversely affected the initial alignment.
It is advantageous to couple a duplex fiber cable to both a source and a detector. A duplex fiber cable includes two optical fibers, each surrounded by appropriate cladding and shielding necessary to eliminate light and/or electromagnetic interference or noise transmission from one fiber to the neighboring fiber. Typically, one of such fibers operates as an output transmission line and is connected to a source, while the other operates as an input transmission line and is connected to a detector. In such a duplex case, active alignment must be performed between one of the two fibers in the duplex fiber cable and the source, and also between the other fiber in the duplex fiber cable and the detector, thus resulting in an even greater possibility of misalignment and lower coupling efficiency.
Additionally, the source and detector are typically positioned directly adjacent one another to accommodate the close proximity of the fibers in the duplex fiber cable. Optical fibers in a standard duplex fiber cable are separated by 2-3 mm. The relative close positioning of source and detector in conventional devices creates a significant electromagnetic interference problem between the two devices because the source emits a level of electromagnetic energy that is significantly greater than the level of electromagnetic energy typically received by the detector. This problem worsens as the data transmission rate is increased. Additionally, the close proximity of the two fibers in the vicinity of the devices can create additional electromagnetic interference.